Zoroastrianism

noun

Zoroastrianism [uncountable]

an ancient religion from Persia (=modern Iran), whose followers believe that there is a continual battle between the forces of good (or light) and the forces of evil (or darkness), but that good will win in the end and humans must help this to happen. The religion is now practised by only a small number of people, most of whom are Parsees living in India.

—Zoroastrianadjective

Definition from the Longman Dictionary of Contemporary English Advanced Learner's Dictionary.